System and method for mobile terminal initiated satellite communications

ABSTRACT

A system and method for improving efficiency of satellite communications is described. In one embodiment, efficient satellite communications is enabled through event-driven reporting by a mobile terminal.

This application claims priority to provisional application No.60/688,685, filed Jun. 9, 2005, which is incorporated herein byreference in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates generally to satellite communicationsystems and methods and, more particularly, to a system and method forevent-driven satellite communications.

2. Introduction

Tracking mobile assets represents a growing enterprise as companies seekincreased visibility into the status of a service fleet (e.g., long-hauldelivery fleet). Visibility into the status of a service fleet can begained through mobile terminals that are affixed to service vehicles.These mobile terminals can be designed to generate position informationthat can be used to update status reports that are provided to customerrepresentatives.

In generating status reports to a centralized facility, the mobileterminal can generate position information through the reception ofsatellite position signals such as that generated by the GPS satellitenetwork. Processing these GPS signals, generating position information,and transmitting status reports to the centralized facility comes at theexpense of the power requirements at the mobile terminal. Here, anincreased number of reporting cycles reduces the effective battery lifeof the mobile terminal, thereby increasing the maintenance and fieldcosts of the mobile terminals. Thus, what is needed is a system andmethod for increasing visibility into the mobile assets, whilemaintaining a reasonable battery life of the mobile terminal.

SUMMARY

The present invention meets the above-mentioned needs by providing asystem and method for improving efficiency of satellite communications.In one embodiment, efficient satellite communications is enabled throughevent-driven reporting by a mobile terminal.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will become more fullyapparent from the following description and appended claims, or may belearned by practice of the invention as set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered limiting of its scope, the invention will be describedand explained with additional specificity and detail through the use ofthe accompanying drawings in which:

FIG. 1 illustrates an embodiment of a satellite communications networkthat enables the monitoring of remote assets.

FIG. 2 illustrates an embodiment of a carousel of timeslots.

FIG. 3 illustrates a flowchart of a communication process of the presentinvention.

DETAILED DESCRIPTION

Various embodiments of the invention are discussed in detail below.While specific implementations are discussed, it should be understoodthat this is done for illustration purposes only. A person skilled inthe relevant art will recognize that other components and configurationsmay be used without parting from the spirit and scope of the invention.

In accordance with the present invention, a system and method isprovided that enables the sending of unscheduled reports by a mobileterminal to an operations center. These unscheduled reports can be on anon-demand or event driven basis. One example of an event is when amobile asset either starts or stops moving. As would be appreciated anysensor (e.g., motion sensor, door sensor, volume sensor, environmentsensor, etc.) can be used to generate a mobile terminal event thatinitiates the formulation and transmission of an unscheduled report.

In supporting start/stop events, the mobile terminal can be designed toinclude a motion sensor that is used to detect movement of assets andinitiate GPS signal measurements for position determination. The motionsensor also aids in the determination of arrival and departure times.One example of an adaptive motion sensor is provided in U.S. patentapplication Ser. No. 11/377,653, entitled “System and Method forAdaptive Motion Sensing with Location Determination,” which isincorporated herein by reference in its entirety.

FIG. 1 describes a communications network that enables a mobile terminalto deliver reports to an operations center. As illustrated, satellitenetwork 100 includes operations gateway 102, communicating withsatellite gateway 104, and has one forward and one return link(frequency) over satellite 106 to mobile terminal 120 located on theasset. From there, operations gateway 102 passes the information tooperation center 112, where the information is used to solve forposition and present the position information to the customer via theinterne. A detailed description of this process is provided in U.S. Pat.No. 6,725,158, entitled “System and Method for Fast Acquisition PositionReporting Using Communication Satellite Range Measurement,” whichincorporated herein by reference in its entirety.

It should be noted that the principles of the present invention can alsobe applied to other satellite-based or terrestrial-based locationdetermination systems where the position is determined at the mobileterminal independently, or at the mobile terminal in combination withinformation received from another location. Further as noted above, theprinciples of the present invention can be applied to events generatedby any of a variety of sensor.

In the example of FIG. 1, mobile terminal 120 can also include a sensor.In this example, adaptive motion sensor 126 is used. The task ofadaptive motion sensor 126 is to determine whether an asset is moving ornot. From there, together with the mobile terminal processor (not shown)and GLS component 124 it can determine the arrival and departure timesand locations of an asset. When an asset begins to move, adaptive motionsensor 126 detects the motion or vibration and sends a signal to themobile terminal processor informing it that motion has started. Themobile terminal processor then records the time motion started, andsignals to GLS component 124 to collect code phase. The start time andthe codephase are sent over the satellite back to operations gateway 102and operation center 112 where the codephase is used to solve forposition, and the start time is used to generate the departure time.Conversely, when adaptive motion sensor 126 determines motion hasstopped it will again inform the mobile terminal processor to collecttime and codephase, and send the information back to operations gateway102. Operation center 112 solves for position, and the stop time is usedto generate the arrival time. The arrival and departure times along withtheir locations can be supplied to the user via the Internet. As noted,in an alternative embodiment, the mobile terminal could send a positiondetermined at the mobile terminal back to operations center 112.

In one embodiment, the protocol supporting communications to and frommobile terminal 120 is a circuitless, packet-based protocol. Thisprotocol can support scheduled or unscheduled reports, depending on theinformation required and the resources available. Scheduled reportintervals can vary from less than a minute to a day, as desired. Theprotocol can also support gateway polling of specified mobile terminalsto deliver commands or obtain information specified in the page. Pagesto a mobile terminal may be either available at defined intervals,accommodating mobile terminal sleep modes, or on a continuouslyavailable basis, depending on mobile terminal monitoring capability. Asnoted, the protocol can also support unsolicited reports from mobileterminals, which may be used to report events, mobile terminaloriginated traffic, or other requirements. The protocol includes errorchecking and correction and both packet and external applicationacknowledgements, facilitating retries if desired.

In one embodiment, the protocol uses a demand-assigned time divisionmultiplexed scheme, called a carousel, for interleaving multiple channeltypes on a frequency allocation on a beam over the communicationssatellite. Multiple simultaneous carousels on different frequencyallocations within one or more satellite beams can be defined. Thecarousel can be designed to broadcast information to the mobileterminals describing the current carousel configuration along withpointers to guide the mobile terminal in a search for other carousels onthe same beam or on other beams if needed.

The carousel can be implemented as a scheduled, cyclically repeatingdefined sequence of defined timeslots used to support communications toand from the mobile terminal. Communications between a large number ofmobile terminals and the network are interleaved over the carousel insuch a way as to provide the assignments yielding the bandwidth andtimeliness necessary for each mobile terminal's operations. Thisstructure facilitates communications while minimizing mobile terminalpower consumption.

In one embodiment, the carousel is composed of 57,600 time slots per dayand repeats each day. Each timeslot carries a packet of 165 bits. Thetimeslots are grouped into 900 frames (numbered sequentially from zeroto 899) of 64 timeslots each. FIG. 2 illustrates the structure of aframe. Timeslot IDs run from 0 to 63 and frame boundaries occur at thebeginning of the zero timeslot. Each timeslot is 1.5 seconds and eachframe is 96 seconds. The period of the carousel is one day. In oneembodiment, the carousel obtains its timing from Coordinated UniversalTime, which synchronizes all elements of the system.

Carousels have both forward and return links. The forward link carriestraffic from the gateway to the mobile terminal, whereas the return linkcarries traffic from the mobile terminal to the gateway. Multiplecarousels may operate at the same time over a given beam of a satellite,each one having a forward link and a return link assigned to it at itsown frequencies.

In one embodiment, the satellite waveform is implemented in a TimeDivision Multiplex (TDM) structure on the forward direction and a TimeDivision Multiple Access (TDMA) structure in the return direction. Onthe forward link, operations gateway 102 sends a message or packet tomobile terminal 120 on one of the 1.5 second slots to give instructionsto global locating system (GLS) component 124 via satellite modemprocessor 122. One example is to instruct GLS component 124 to perform aGPS collection (e.g., code phase measurements) and transmit the databack to operations gateway 102. When GLS component 124 of mobileterminal 120 receives this forward command, it collects the GPSinformation and transmits the data back on the return link, on the sameslot, delayed by a fixed time defined by the network. The delay isneeded to decode the forward packet, perform the GPS collect andprocessing, and build and transmit the return packet.

Each frame is a sequence of 64 timeslots. It begins with a SystemBroadcast (SB) channel timeslot (timeslot 0) followed by a BeamBroadcast (BB) channel timeslot (timeslot 1).

The SB channel carries information about the carousel within which it iscarried. It enables mobile terminals to gather information they need inorder to operate effectively within the carousel. For example, a packetwithin the SB channel can include timing information, frame number,satellite number, carousel identity number, congestion level of thepresent carousel, and timeslot designation parameters for channelswithin the carousel.

The BB channel carries information that enables mobile terminal roamingbetween beams on the satellite. For example, a packet within the BBchannel can include the carousel's forward frequencies on all otherbeams, the carousel's return frequencies for all other beams, the beamidentity number, and GPS satellite identifiers for GPS satellites to beused within the area served by the beam.

Additional channel types can be assigned to the remaining 62 timeslotswithin a frame. As noted, a packet on the SB channel can designate thestructure of the frame's last 62 timeslots, identifying the particularchannel types. The different number of channel types supporting variousfunctions can be varied in size to respond to relative demand, or evendisabled and released for other uses if not needed.

In general, a channel can be viewed as an established series oftimeslots in the carousel that constitute an on-going set oftransmission opportunities for a specific type of traffic. In additionto the SB and BB channels, a Position/State (PS) channel and anEvent/Registration (ER) channel can also be defined.

The PS channel carries scheduled position and/or state polls directed tomobile terminals in the forward direction and responses from the mobileterminals in the same timeslot in the return direction. Packets on thePS channel generally identify one or more mobile terminals that arescheduled to report together with identifiers of GPS satellite to beused. In the return direction the mobile terminal responds with codephase data along with other data (e.g., sensor data) on its currentstate as appropriate.

The ER channel, on the other hand, provides for unscheduled, mobileterminal initiated communications, including position and/or sensordata, with the gateway in the return direction. Gateway responses oracknowledgements to the respective mobile terminal are carried in theforward direction.

The system assigns each channel a sequence of timeslots in the frame,which repeat from frame to frame. Channels are typically interleaved inslot assignments to achieve desirable latency characteristics for eachchannel; however, this need not necessarily be true.

Gateways transmit a packet on every timeslot of the day in eachcarousel, and so essentially transmit full period. If no other packet isdesignated for transmission in a given timeslot, the gateway willtransmit a No-Op (NO) packets in that slot. NO packets include somesystem data and the list of satellites in view to aid mobile terminalsin staying current.

As noted, the timeslots 0 and 1 are reserved for SB and BB packets.Other timeslots in the frame may be designated for either PS or ERpackets. Frame definitions are generally static from frame to frame, butcan be changed, for example, to rebalance or optimize traffic on thecarousel

On any given PS channel timeslot, the gateway normally transmits PSpayloads to a mobile terminal of a given mobile terminal address (MTA)assigned to the timeslot unless other traffic is pending. In the latterevent, such traffic may supplant the PS for the slot, and direct themobile terminal to further slots if necessary (including for a report inresponse to a PS if desired).

If the gateway addresses an MTA, but with no accompanying commandidentifying the information desired (perhaps because it is addressingmore than one MT with different requests for each), the mobile terminalcan respond on the appropriate following timeslot with a Request forTraffic (RT) payload, requesting traffic from the gateway. The gatewaywill then make its specific request or instruction known to that mobileterminal in its following response.

In many respects, the gateway is reactive to the mobile terminal. Themobile terminal initiates registration by sending a registration requeston an ER channel, to which the gateway will respond with a registrationassignment. The mobile terminal cannot accept assignments unless it isfirst registered, which also configures the mobile terminal.

Mobile terminals normally awaken to receive traffic, process informationas necessary, transmit traffic, then put themselves back to sleep untilthe next scheduled wake-up. This conserves power, making the mobileterminal very power efficient. Mobile terminals are normally awake foraround 10 seconds, a figure that can be varied as necessary depending onmobile terminal and processing needs.

Mobile terminals respond to commands in the PS channel regarding thepayload type to be sent to the gateway for solicited scheduled traffic.Mobile terminals can be given assignments to awaken on PS channeltimeslots at stated times during a day. A typical mobile terminalassignment might be one PS channel timeslot (report opportunity) per dayto report and 12 slots per day to monitor. PS channel assignments canvary from one per day to one per frame.

As described, PS channels are assigned to mobile terminals and enablemobile terminals to report monitoring results on a scheduled basis.On-demand or event-driven reporting, however, requires a different formof channel assignment and usage to facilitate sporadic reports. This isespecially true where one or more sensors trigger the generation ofincreasing amounts of report traffic.

It is a feature of the present invention that mobile terminals that areawakened on an event basis can transmit reports on a next usabletimeslot that the mobile terminal identifies. Typically, the next usabletimeslot will not be a timeslot assigned to the mobile terminal becausethe mobile terminal has been awakened at an unscheduled time.

FIG. 3 illustrates an embodiment of a process for a mobile terminal toidentify a next usable timeslot. As illustrated, this process begins atstep 302, where the mobile terminal examines the next forward timeslot.The next forward timeslot can be assigned by the system for differentpurposes. For example, the next forward timeslot could support a PSchannel, an ER channel, or some other channel type. In one embodiment,the mobile terminal is configured to search sequentially through thetimeslots on the carousel to identify a timeslot that can be used. Thissequential timeslot search process can begin at any point in time afterthe mobile terminal is awakened. For example, the sequential timeslotsearch process can begin immediately after the mobile terminal isawakened, or after a period of time has elapsed (e.g., after timeslots 0and 1 have been received). It should also be noted that the searchprocess need not consider every single timeslot in a sequence. Invarious embodiments, the search process can search through a subset of ablock of timeslots, wherein the subset represents candidate timeslots.Regardless of the starting point and the timeslots considered, thesearch process is designed to identify a usable timeslot that waspreviously unassigned to the mobile terminal.

At step 304, the mobile terminal determines whether the timeslot isusable. Usability of a timeslot can be determined based on the trafficon the timeslot and the timeslot type. For example, if the mobileterminal determines that the timeslot supports an ER channel (e.g.,based on the information carried on the SB channel on timeslot 0, and byan ERCFlag bit on a packet that is set to 1 if the timeslot is an ERchannel timeslot), then the mobile terminal knows that the timeslotsupports unscheduled, mobile terminal initiated communications with thegateway. If examination of the traffic on the ER channel timeslotsuggests that another mobile terminal will not be using the return linkto transmit a packet to the gateway, then the timeslot can be consideredusable. In another example, the mobile can determine that the timeslotsupports a PS channel. This PS channel may be assigned to another mobileterminal to support scheduled position reports. If the mobile terminaldetermines that a position/state request packet including an MTA is onthe timeslot, then the mobile terminal knows that the timeslot isassigned to another mobile terminal. If the mobile terminal determines,however, that a NO packet is on the timeslot, then the mobile terminalknows that the timeslot is not assigned to another mobile terminal. Thetimeslot can then be considered to be usable. In general, the mobileterminal can examine any timeslot to determine whether the existing useor assignment of such a timeslot precludes the mobile terminal fromconsidering it as a usable timeslot.

If, at step 304, the mobile terminal determines that the timeslot is notusable, then the mobile terminal will consider the next timeslot in theconsidered sequence. As noted above, this next considered timeslot neednot be the immediately following timeslot. In one embodiment, the mobileterminal can be configured to limit the number of timeslots that it willconsider in a sequence. For example, the mobile terminal can beconfigured to search through four timeslots in a sequence. In thisexample, if the fourth timeslot considered is determined not to beusable, then the mobile terminal would enter sleep mode and reawakenafter a defined backoff period.

If, at step 304, the mobile terminal determines that the timeslot isusable, then the mobile terminal transmits the unscheduled report on thecorresponding return timeslot at step 306.

Next, at step 308, the mobile terminal examines traffic on the forwardtimeslot corresponding to the return timeslot on which the unscheduledreport was transmitted. For ER channels, the mobile terminal can examinethe succeeding ER channel forward timeslot offset in time by the numberof ER channel timeslots specified in the event/reporting acknowledgementoffset (ERCAckOS) field in a system packet. For PS channels, the mobileterminal would examine the later forward timeslot that is determinedbased on the payload acknowledgment offset (PldAckOS) field in thesystem packet, which indicates how many time slots earlier contains thepacket being acknowledged.

At step 310, the mobile terminal determines whether an acknowledgmenthas been received from the gateway on the forward timeslot. Thisacknowledgment is important because the unscheduled report is a mobileterminal initiative, and thus the burden is on the mobile terminal toensure its receipt. A received acknowledgment informs the mobileterminal that the unscheduled report has been received. In general, itis possible that more than one mobile terminal may attempt to use thesame timeslot that has been identified as usable. In one embodiment,multiple mobile terminals can transmit narrowband spread spectrumwaveforms on the same usable timeslot. The gateway can then beconfigured to receive unscheduled reports from multiple mobileterminals. For example, if three mobile terminals transmit unscheduledreports on the same usable timeslot, the system may respond to two ofthe three mobile terminals. In this example, acknowledgement of thetransmissions of two of the mobile terminals can be effected through aninclusion of two MTAs in the payload of a single acknowledgement packet.

If it is determined, at step 310, that an acknowledgment has beenreceived, then the unscheduled report has been delivered and the processends.

If, on the other hand, it is determined, at step 310, that anacknowledgment has not been received, then the mobile terminal will lookto retransmit the unscheduled report on a later timeslot. It should benoted that in one embodiment, the mobile terminal can also be configuredto check for acknowledgments in succeeding packets. This could occur,for example, if the mobile terminal transmitted an unscheduled report ona PS channel, wherein the timeslot identified by the PldAckOS field wasneeded by the gateway for other mobile terminal transmissions. In oneembodiment, the identification of another available timeslot will notbegin immediately. Rather, at step 312, the mobile terminal would applya random backoff algorithm designed to minimize repeated collisionsamong mobile terminals and wait for a backoff period before identifyinganother available timeslot.

The mobile terminal can adjust the offset, or delay, to the next retryfor an event transmission to minimize the probability of successivecollisions and maximize mobile terminal power consumption efficiency.Therefore, the mobile terminal can increase the length of the intervalover which it selects a transmission time depending on the number ofpreceding successive acknowledgement failures for earlier transmissionsof the same event payload, the priority of the event, and the cause forthe acknowledgement failure (signal blockage or signal collision).Priority scales the intervals with higher priorities reducing theinterval sizes (lower priority numbers denote higher priority).Collisions prompt randomizing the timeslot selection over the delayinterval rather than using the end of the interval. Collision andnon-collision backoffs may use different scales. Collisions are detectedby detecting a forward payload addressed to a particular mobile terminalother than itself.

These and other aspects of the present invention will become apparent tothose skilled in the art by a review of the preceding detaileddescription. Although a number of salient features of the presentinvention have been described above, the invention is capable of otherembodiments and of being practiced and carried out in various ways thatwould be apparent to one of ordinary skill in the art after reading thedisclosed invention, therefore the above description should not beconsidered to be exclusive of these other embodiments. Also, it is to beunderstood that the phraseology and terminology employed herein are forthe purposes of description and should not be regarded as limiting.

What is claimed is:
 1. A satellite communications method in a mobileterminal, wherein satellite communication between a plurality of mobileterminals and an operation center is supported by a cyclically repeatingdefined sequence of timeslots, said cyclically repeating definedsequence of timeslots including scheduled reporting timeslot types andunscheduled reporting timeslot types, said scheduled reporting timeslottypes capable of being assigned to individual mobile terminals, themethod comprising: transitioning from a low power state to an activestate at a time proximate to a timeslot of a scheduled reportingtimeslot type that has been assigned to said mobile terminal; aftertransitioning from said low power state to said active state, firsttransmitting, via a communication satellite, a scheduled report to saidoperation center on said timeslot of said scheduled reporting timeslottype; after said first transmitting, transitioning from said activestate to said low power state; detecting an occurrence of an unscheduledevent by said mobile terminal; transitioning from said low power stateto said active state upon detection of said occurrence of saidunscheduled event; after transitioning from said low power state to saidactive state, sequentially analyzing a first plurality of timeslots thatincludes timeslots of said scheduled reporting timeslot type and saidunscheduled reporting timeslot type, said analyzing of said plurality oftimeslots including an analysis of traffic on timeslots of saidscheduled reporting timeslot type; identifying, based on said sequentialanalysis of said first plurality of timeslots, a first usable timeslotin said first plurality of timeslots, said identified first usabletimeslot not being previously assigned to said mobile terminal;transmitting, via said communication satellite, an unscheduled reportbased on said detected occurrence of said unscheduled event on saididentified first usable timeslot; if an acknowledgment of saidtransmitted unscheduled report is not received, then sequentiallyanalyzing a second plurality of timeslots that begins at a point in saidcyclically repeating defined sequence of timeslots greater than abackoff period, said second plurality of timeslots including timeslotsof said scheduled reporting timeslot type and said unscheduled reportingtimeslot type, said analyzing of said second plurality of timeslots alsoincluding an analysis of traffic on timeslots of said scheduledreporting timeslot type, wherein at least two of said second pluralityof timeslots are consecutive timeslots that are analyzed in consecutiveorder; identifying, based on said sequential analysis of said secondplurality of timeslots, a second usable timeslot in said secondplurality of timeslots, said identified second usable timeslot not beingpreviously assigned to said mobile terminal; and retransmitting saidunscheduled report on said identified second usable timeslot.
 2. Themethod of claim 1, further comprising determining, after saidtransmission of said unscheduled report, whether an acknowledgment ofsaid transmission of said unscheduled report is received from saidoperation center.
 3. The method of claim 2, further comprisingretransmitting said unscheduled report on a second identified usabletimeslot if it is determined that an acknowledgement is not received. 4.The method of claim 1, wherein said identifying comprises identifying atimeslot of an unscheduled reporting timeslot type.
 5. The method ofclaim 1, wherein said identifying comprises identifying a timeslot of ascheduled reporting timeslot type that is not currently assigned to amobile terminal.
 6. The method of claim 1, wherein said transmittingcomprises transmitting, via said communication satellite, a narrowbandspread spectrum waveform on said identified usable communicationtimeslot.
 7. The method of claim 1, wherein said timeslots are timedivision multiplexed timeslots.
 8. A satellite communications method ina mobile terminal, wherein satellite communication between a pluralityof mobile terminals and an operation center is supported by a cyclicallyrepeating defined sequence of timeslots, said cyclically repeatingdefined sequence of timeslots including scheduled reporting timeslottypes and unscheduled reporting timeslot types, said scheduled reportingtimeslot types capable of being assigned to individual mobile terminals,the method comprising: detecting an occurrence of an unscheduled eventby said mobile terminal; transitioning from a low power state to anactive state upon detection of said occurrence of said unscheduledevent; after transitioning from said low power state to said activestate, sequentially analyzing a first plurality of timeslots thatinclude timeslots of said scheduled reporting timeslot type and saidunscheduled reporting timeslot type, said analyzing including ananalysis of traffic on timeslots of said scheduled reporting timeslottype; identifying, based on said sequential analysis of said firstplurality of timeslots, a first usable timeslot in said first pluralityof timeslots, said first identified usable timeslot not being previouslyassigned to said mobile terminal; transmitting, via a communicationsatellite, an unscheduled report based on said detected occurrence ofsaid unscheduled event on said first identified usable timeslot;determining, after said transmission of said unscheduled report, whetheran acknowledgment of said transmission of said unscheduled report isreceived from said operation center; when it is determined that saidacknowledgment is not received, sequentially analyzing a secondplurality of timeslots that include timeslots of said scheduledreporting timeslot type and said unscheduled reporting timeslot type,said second plurality of timeslots beginning at a point determined usinga backoff period, wherein at least two of said second plurality oftimeslots are consecutive timeslots that are analyzed in consecutiveorder; identifying, based on said sequential analysis of said secondplurality of timeslots, a second usable timeslot in said secondplurality of timeslots, said second identified usable timeslot not beingpreviously assigned to said mobile terminal; and retransmitting, viasaid communication satellite, said unscheduled report on said secondidentified usable timeslot.
 9. The method of claim 8, wherein saidbackoff period is determined based on a priority measure.
 10. The methodof claim 8, wherein said identifying comprises identifying a timeslot ofan unscheduled reporting timeslot type.
 11. The method of claim 8,wherein said identifying comprises identifying a timeslot of a scheduledreporting timeslot type that is not currently assigned to a mobileterminal.
 12. The method of claim 8, wherein said transmitting comprisestransmitting, via said communication satellite, a narrowband spreadspectrum waveform on said identified usable communication timeslot. 13.The method of claim 8, wherein said timeslots are time divisionmultiplexed timeslots.